Abstract

We aim to solve a structured convex optimization problem, where a nonsmooth function is composed with a linear operator. When opting for full splitting schemes, usually, primal–dual type methods are employed as they are effective and also well studied. However, under the additional assumption of Lipschitz continuity of the nonsmooth function which is composed with the linear operator we can derive novel algorithms through regularization via the Moreau envelope. Furthermore, we tackle large scale problems by means of stochastic oracle calls, very similar to stochastic gradient techniques. Applications to total variational denoising and deblurring, and matrix factorization are provided.

Highlights

  • The problem at hand is the following structured convex optimization problem min f (x) + g(K x), (1)x ∈H for real Hilbert spaces H and G, f : H → R := R ∪ {±∞} a proper, convex and lower semicontinuous function, g : G → R a, possibly nonsmooth, convex and Lipschitz continuous function, and K : H → G a linear continuous operator.Research partially supported by FWF (Austrian Science Fund) project I 2419-N32

  • Research supported by the doctoral programme Vienna Graduate School on Computational Optimization (VGSCO), FWF (Austrian Science Fund), Project W 1260

  • The approach can be described as follows: we “smooth” g, i.e. we replace it by its Moreau envelope, and solve the resulting optimization problem by an accelerated proximal-gradient algorithm

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Summary

Introduction

The problem at hand is the following structured convex optimization problem min f (x) + g(K x),. X ∈H for real Hilbert spaces H and G, f : H → R := R ∪ {±∞} a proper, convex and lower semicontinuous function, g : G → R a, possibly nonsmooth, convex and Lipschitz continuous function, and K : H → G a linear continuous operator. Research partially supported by FWF (Austrian Science Fund) project I 2419-N32. Research supported by the doctoral programme Vienna Graduate School on Computational Optimization (VGSCO), FWF (Austrian Science Fund), Project W 1260

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Preliminaries
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Deterministic Method
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Stochastic Method
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Numerical Examples
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Total Variation Denoising
Total Variation Deblurring
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Matrix Factorization
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